As shown in FIGS. 5–8, a prior art nail gun comprises a body 60, which is provided with an upright slot 62 to accommodate an explosive array 61 in such a manner that the explosive array 61 can be caused to move up and down along the upright slot 62 by a cooperative effort of a movable arm 63, a link rod 64 and an actuation rod 65. The movable arm 63 is pivoted at a pivoting point 66 with a barrel 67 and is provided with a nail loading hole 68. As the movable arm 63 is swivelled forward for an angle of 180 degrees, the movable arm 63 is aligned with the barrel 67 so as to enable the nail to be loaded in the barrel 67 by means of a slide seat 69 which is pivoted with the movable arm 63. The link rod 64 and the actuation rod 64 are disposed in a horizontal chamber 70 such that the link rod 64 is pivoted with the movable arm 63, and that an inverted hook 652 of the actuation rod 65 is retained in one of the retaining slots 611 of the explosive array 61. The actuation rod 65 is provided with a V-shaped through hole 653 in which a pin of the link rod 64 is movable received. Each time when a nail is discharged, the movable arm 63 must be swivelled forward and backward, so as to complete the loading of another nail and to position another explosive cavity 612 of the explosive array 61. It is therefore readily apparent that the prior art nail gun is inefficient at best.